All animals and plants produce antibacterial peptides, which are major effector molecules of innate immunity. More than 700 antibacterial peptides are known. Antibacterial peptides are natural bactericidal components that are similar in potency to classical antibiotics.
All antibacterial peptides from animals are gene encoded and the primary transcript is translated into an inactive precursor that needs proteolytic processing to become a bactericidal effector. The use of an inactive precursor is thought to protect the host cells from damage and may be an important regulatory mechanism.
In humans, antibacterial peptides are produced at all body surfaces by epithelial cells, specialized granular cells and white blood cells. Most species have families of several rather similar peptides, each with their own genes. This is thought to be an evolutionary safeguard against deleterious mutations. Two major families of the human repertoire of antibacterial peptides are the α- and β-defensins. Granulated cells such as Paneth cells and neutrophils produce α-defensins while β-defensins are mainly produced by epithelial cells. LL-37, encoded by the CAMP gene is the only cathelicidin type peptide that has been identified in humans. LL-37 is produced by neutrophils and to a lesser extent by peripheral lymphocytes. Skin and gingiva also express LL-37. The proform of LL-37 is cathelin-LL-37 which is cleaved, for example upon neutrophil excitation, to release the bactericidal peptide LL-37.
Morbus Kostmann is a severe congenital neutropenia here defined as the disease in descendants of the original Kostmann family. Morbus Kostmann arises as a result of a recessive mutation and differs from most other inherited neutropenia which are thought to be due to dominant mutations in the gene for elastase. The origin of the autosomal recessive neutropenia morbus Kostmann is not known. The undefined gene defect(s) results in a neutrophil maturation arrest at the promyelocyte/myelocyte stage.
The Kostmann syndrome was fatal up to around 1975 when modern antibiotics were introduced. Since around 1990, when recombinant granulocyte colony stimulating factor (G-CSF) became available, an improved treatment with recombinant human G-CSF has been practiced. This involves daily injections of G-CSF combined with antibiotic therapy when necessary. The G-CSF treatment restores the number of neutrophils to normal levels and this has dramatically improved the quality of life for these patients. However, in spite of the corrected neutrophil levels, Kostmann patients are still prone to infections and suffer from severe periodontal disease.